Oxirane compounds such as ethylene oxide, propylene oxide, and their higher homologs are valuable articles of commerce. One of the most attractive processes for synthesis of those oxirane compounds is described by Kollar in U.S. Pat. No. 3,351,635. According to Kollar, the oxirane compound (e.g., propylene oxide) may be prepared by epoxidation of an olefinically unsaturated compound (e.g., propylene) by use of an organic hydroperoxide and a suitable catalyst such as molybdenum.
During the epoxidation reaction the hydroperoxide is converted almost quantitatively to the corresponding alcohol. That alcohol may be recovered as a coproduct with the oxirane compound. However, it is the oxirane which is of primary concern.
Kollar teaches that oxirane compounds may be prepared from a wide variety of olefins. Lower olefins having three or four carbon atoms in an aliphatic chain are advantageously epoxidized by the process. The class of olefins commonly termed alpha olefins or primary olefins are epoxidized in a particularly efficient manner by the process. It is known to those in the art that primary olefins, e.g., propylene, butene-1, decene-1, hexadecene-1, etc., are much more difficultly epoxidized than other forms of olefins, excluding only ethylene. Other forms of olefins which are much more easily epoxidized are substituted olefins, alkenes with internal unsaturation, cycloalkenes and the like. Kollar teaches that notwithstanding the relative difficulty in epoxidizing primary olefins, epoxidation proceeds more efficiently when molybdenum, titanium or tungsten catalysts are used. Molybdenum is of special interest. Kollar teaches that activity of those metals for epoxidation of primary olefins is surprisingly high and can lead to high selectivity of propylene to propylene oxide. These high selectivities are obtained at high conversions of hydroperoxide (50% or higher) which conversion levels are important for commercial utilization of the technology.
Kollar's epoxidation reaction proceeds under pressure in the liquid state and, accordingly, a liquid solution of the metal catalyst is preferred. Preparation of a suitable catalyst is taught by Sheng et al in U.S. Pat. No. 3,434,975. According to Sheng, the reaction-medium soluble epoxidation catalyst may be prepared by reacting molybdenum metal with an organic hydroperoxide, peracid or hydrogen peroxide in the presence of a saturated alcohol having one to four carbon atoms.
Another molybdenum epoxidation catalyst is described by Bonetti et al in U.S. Pat. No. 3,480,563. Bonetti teaches that molybdenum trioxide may be reacted with a primary saturated acyclic alcohol having 4 to 22 carbon atoms or with a mono- or polyalkylene glycol monoalkyl ether. The reaction involves heating the molybdenum trioxide in the alcohol or ether to produce an organic soluble molybdenum catalyst.
Maurin et al in U.S. Pat. No. 3,822,321 describes oxidizing olefins with a hydroperoxide using a molybdenum catalyst prepared by reacting a molybdenum compound such as molybdic acid or a molybdic salt with a polyalcohol.
A molybdenum catalyzed epoxidation of olefins is described by Lines et al in U.S. Pat. No. 4,157,346. The catalyst is prepared by reacting an oxygen containing molybdenum compound with an amine (or an amine N-oxide) and alkylene glycol.
British Pat. No. 1,060,122 is concerned with an epoxidation reaction employing catalytic quantities of a molybdenum catalyst which is in the form of an inorganic molybdenum compound.
French Pat. No. 1,550,166 discloses that the molybdic acid esters, and especially glycol esters of molybdic acid, provide certain advantages over previously known catalysts to effect epoxidation employing organic hydroperoxides for reaction with olefinic compounds.
In U.S. Pat. No. 3,887,361 Lemke discloses that spent catalyst solutions obtained from the process of epoxidation of olefins with hydroperoxides in the presence of molybdenum may be treated to precipitate and separate dissolved molybdenum. The Lemke process involves mixing spent catalyst solution with 5 to 50 parts by weight of tertiary-butyl alcohol and heating the mixture to between 100.degree. and 300.degree. C. in a closed vessel or under reflux, thereby resulting in precipitation of molybdenum as a finely divided solid. The solid is disclosed to be suitable for recycle into further epoxidation reactions, as such, or optionally, after dissolution in an organic acid or an acid obtained in the "Oxo process" for production of oxygenated organic derivatives. The Lemke solids typically contain about 30 to about 40 percent by weight of molybdenum.